The rear frame crossmember of the GX is a "crash bar" with many large holes drilled in it. I would expect the crash bar is crumpled to some degree, and in fact may have taken most of the impact from the accord (it's intended to bend and absorb energy instead of transmitting it into the vehicle and the occupants). The rear frame rails of the GX are actually kind of thin 1/8" steel, so it's possible the impact coupled with the rigid trailer hitch may have bent them. The rear crash bar is available as a new part for Lexus and can pretty easily be replaced by a body shop (it comes off by cutting a few welds), but if the rear frame rails are bent I'd expect them to total it.
Even if it's not totaled, I'd expect the damage to easily exceed $10K considering you are going to need both bumpers, a rear hatch, paint, and probably some other things as well. If they offer to total the rig and give you a reasonable payment for it, I'd personally take it and find another GX that hasn't been hit. It will take an A+ shop to get it back together anywhere near as good as it came out of the factory, and the color is going to be quite difficult to match as well.
Also I have to ask - distracted driver? Can't imagine any other reason why someone would slam into a row of cars sitting at a red light.